1. Technical Field
This invention relates to ferrite shielding toroids as applied on cables. In particular, it relates to an apparatus for retaining one or more ferrite shielding toroids in a stationary arrangement on a cable.
2. Background Art
Ferrite shielding toroids, or as hereinafter referred to as ferrite toroids serve two purposes when surrounding an electrical wire or cable. Firstly, they provide a mechanism for shielding the wire or cable from a hostile magnetic environment. Secondly, they provide a low pass filter which attenuates frequencies in the megahertz range, normally between 10 and 100 MHz. By fitting a wire or cable with a ferrite toroid, a small inductor is constructed. The magnetic field of the ferrite toroid interacts with the magnetic field created by the current in the cable and any hostile magnetic fields in the immediate environment. The ferrite toroid essentially provides a lossy impedance in the cable which acts to decouple the cable from high frequencies.
A typical application might be in a computer printer, which has associated with it hostile high frequency magnetic fields, as do most high speed switching digital devices. The use of ferrite toroids for shielding the electrical lines in such an environment is old and well known. However, a unique situation arises in that wires and cables subject to motion and vibration which are fitted with ferrite toroids are prone to chafing of the cable insulation by the ferrite toroids. This results in deterioration of the insulation and eventually warrants replacement of the wiring.
LEITNER, ET AL., U.S. Pat. No. 3,680,146 teaches a high frequency antenna system which utilizes a plurality of ferrite toroids for the purpose of suppressing electromagnetic radiation. LEITNER teaches ferrite toroids having an inside diameter slightly larger than the outside diameter of the coaxial cable. This method is not new and is commonly used in a variety of individual applications. The problem with this method of fitting a cable with a ferrite toroid is that cables which are subject to vibration and movement experience chafing of their insulation by the ferrite toroids. Simply reducing the inside diameter of the ferrite toroids and thereby facilitating a snugger fit will not work because the ferrite toroid must be slid along the outside surface of the cable from a disconnected end to its final destination.
Accordingly, what is needed is an apparatus which holds a ferrite toroid in a stable position around the circumference of a cable and which prohibits the ferrite toroid from touching the insulation, thereby eliminating chafing problems. It is an object of this invention to provide a means for engaging a ferrite toroid in a stationary position around the circumference of a cable and at the same time prohibiting the ferrite toroid from contacting the insulation of the cable. A further object of the present invention is to provide a resilient apparatus capable of frictional engagement around the circumference of a cable which is easily installed and does not restrict the flexibility of the cable.